Not positive, but assuming when you state "fails to extract" your actually meaning fails to feed (or that round fails to leave the magazine).
Sounds like feed-lip problems, how old are these mags?
BTW, alloy mag followers are all you'll find on 20 round mags, as green followers require modification in order to work in 20 rounders.
Suggest ya purchase 1 good 20 rounder from somebody like GPSS (Georgia Precision Shooting Supply) on-site here (Industry forum or EE), then when it arrives you can compare lips and assembly with a good one. I have heard of mag springs getting reversed on follower and causing problems, but generally speaking 20 rounders are far more reliable than the 30s.
Suggest ya do a complete disassembly on the problem mags to check springs and thoroughly clean inside of mag bodies.
Hope this is some help,
Mike